stm32: read microsecond from RTC

embassy-stm32/src/rtc/datetime.rs

@@ -21,6 +21,8 @@ pub enum Error {
     InvalidMinute,
     /// The [DateTime] contains an invalid second value. Must be between `0..=59`.
     InvalidSecond,
+    /// The [DateTime] contains an invalid microsecond value. Must be between `0..=999_999`.
+    InvalidMicrosecond,
 }
 
 /// Structure containing date and time information
@@ -39,6 +41,8 @@ pub struct DateTime {
     minute: u8,
     /// 0..59
     second: u8,
+    /// 0..999_999
+    usecond: u32,
 }
 
 impl DateTime {
@@ -77,6 +81,11 @@ impl DateTime {
         self.second
     }
 
+    /// Get the microsecond (0..=999_999)
+    pub const fn microsecond(&self) -> u32 {
+        self.usecond
+    }
+
     /// Create a new DateTime with the given information.
     pub fn from(
         year: u16,
@@ -86,6 +95,7 @@ impl DateTime {
         hour: u8,
         minute: u8,
         second: u8,
+        usecond: u32,
     ) -> Result<Self, Error> {
         if year > 4095 {
             Err(Error::InvalidYear)
@@ -99,6 +109,8 @@ impl DateTime {
             Err(Error::InvalidMinute)
         } else if second > 59 {
             Err(Error::InvalidSecond)
+        } else if usecond > 999_999 {
+            Err(Error::InvalidMicrosecond)
         } else {
             Ok(Self {
                 year,
@@ -108,6 +120,7 @@ impl DateTime {
                 hour,
                 minute,
                 second,
+                usecond,
             })
         }
     }
@@ -124,6 +137,7 @@ impl From<chrono::NaiveDateTime> for DateTime {
             hour: date_time.hour() as u8,
             minute: date_time.minute() as u8,
             second: date_time.second() as u8,
+            usecond: date_time.and_utc().timestamp_subsec_micros(),
         }
     }
 }
@@ -133,7 +147,12 @@ impl From<DateTime> for chrono::NaiveDateTime {
     fn from(date_time: DateTime) -> Self {
         NaiveDate::from_ymd_opt(date_time.year as i32, date_time.month as u32, date_time.day as u32)
             .unwrap()
-            .and_hms_opt(date_time.hour as u32, date_time.minute as u32, date_time.second as u32)
+            .and_hms_micro_opt(
+                date_time.hour as u32,
+                date_time.minute as u32,
+                date_time.second as u32,
+                date_time.usecond,
+            )
             .unwrap()
     }
 }

embassy-stm32/src/rtc/mod.rs

@@ -59,7 +59,7 @@ impl RtcTimeProvider {
     ///
     /// Will return an `RtcError::InvalidDateTime` if the stored value in the system is not a valid [`DayOfWeek`].
     pub fn now(&self) -> Result<DateTime, RtcError> {
-        self.read(|dr, tr, _| {
+        self.read(|dr, tr, _ss| {
             let second = bcd2_to_byte((tr.st(), tr.su()));
             let minute = bcd2_to_byte((tr.mnt(), tr.mnu()));
             let hour = bcd2_to_byte((tr.ht(), tr.hu()));
@@ -69,7 +69,17 @@ impl RtcTimeProvider {
             let month = bcd2_to_byte((dr.mt() as u8, dr.mu()));
             let year = bcd2_to_byte((dr.yt(), dr.yu())) as u16 + 2000_u16;
 
-            DateTime::from(year, month, day, weekday, hour, minute, second).map_err(RtcError::InvalidDateTime)
+            // Calculate second fraction and multiply to microseconds
+            // Formula from RM0410
+            #[cfg(not(rtc_v2f2))]
+            let us = {
+                let prediv = RTC::regs().prer().read().prediv_s() as f32;
+                (((prediv - _ss as f32) / (prediv + 1.0)) * 1e6).min(999_999.0) as u32
+            };
+            #[cfg(rtc_v2f2)]
+            let us = 0;
+
+            DateTime::from(year, month, day, weekday, hour, minute, second, us).map_err(RtcError::InvalidDateTime)
         })
     }
 

examples/stm32g0/src/bin/rtc.rs

@@ -15,7 +15,7 @@ async fn main(_spawner: Spawner) {
 
     info!("Hello World!");
 
-    let now = DateTime::from(2023, 6, 14, DayOfWeek::Friday, 15, 59, 10);
+    let now = DateTime::from(2023, 6, 14, DayOfWeek::Friday, 15, 59, 10, 0);
 
     let mut rtc = Rtc::new(p.RTC, RtcConfig::default());